OSTEOLOGY OF THE ARMORED DINOSAXJRIA. 75 



Metacarpal V (pi. 21, fig. 2) is the weakest element of this series, although 

 this does not imply at all that it is vestigal. It may be recognized at once by the 

 straightness of its outer border and by the hook-like process developed on the internal 

 side of the distal end (5, pi. 21, fig. 2). The shaft is moderately^constricted ; the 

 distal end is rounded antero-posteriorly, widest on the external side, narrowing 

 toward the inner, as does the whole bone. The inner border cf the proximal end is 

 slightly concave where it meets metacarpal IV. The posterior side lacks the strong 

 ridge, with roughened surface, which is so prominent a feature in metacarpals II, 

 III, and IV. 



An outline drawing (fig. 39) of the proximal ends of the metacarpals shows 

 that when articulated their triangular ends combine to form a compact semi- 

 circular foot well adapted for supporting the great weight of the body. There is 

 no interlocking of the metacarpals as found in the feet of some dinosaurs, but this 

 apparent mechanical weakness is compensated for by the increased size of the 

 muscles and ligaments which bound the foot together, as indicated by the rugosity 

 of the areas for their attachment. In the shortness of the metacarpals, depth of 

 carpus, and arch of the foot, there is a striking superficial resemblance to the foot 

 of the elephant. 



Phalanges. — The phalangial formula yet remains to be determined. Of the 

 proximal row of phalanges, only those pertaining to digits I, III, and IV have been 

 found in place. In the left fore foot of specimen No. 4937 the first phalanx of digit 

 I was found attached by matrix to the metacarpal, and in the foot of the same 

 side of S. stenops, No. 4934, the first phalanges of digits III and IV were found 

 similarly attached (fig. 40). 



This constitutes all of the definite evidence as to the correct placing of the 

 phalangial elements. With specimen No. 7401 (see fig. 37), a disarticulated foot, 

 there are six phalangial bones preserved, two of which are unguals. With the 

 right fore foot of No. 4937 there are five phalanges, one of which is terminal. Four 

 of these have been regarded as constituting the proximal row as shown in figure 38. 



The proximal phalanx of the first digit is undoubtedly the largest element of 

 this row. It is wider than long, with posterior articular surface concave and ante- 

 rior convex in the vertical direction. Both upper and lower surfaces concave lon- 

 gitudinally, the upper being convex, the lower concave transversely. The inner 

 side is longer than the outer, and when articulated makes it appear wedge-shaped 

 with the point directed toward the opposite foot. 



In the half-grown animal the inner fourth of this bone is much depressed as 

 shown by specimen No. 7401. The first phalanx of digit II is not certainly known. 



The proximal phalanx of digits III and IV will be described from No. 4934 

 where they were found in place. They are short bones, wider than long, with 

 concave proximal, and convex distal articular ends. The palmar surfaces are 

 flattened and produced posteriorly into a thin sheet which lies under the ends 

 of the metacarpals when articulated. Viewed superiorly the first phalanx of 

 digit IV presents a longer concave surface than the phalanx of digit III, but 

 the distal articulating surface is considerably reduced in size, and with a distinct 

 articular protuberance on the internal side of this surface, reminding one of the 



